Half controlled single bridge rectifier

In summary, the conversation discussed the operation of a half-controlled single bridge rectifier with an R-L load and a firing angle 'alpha'. The question posed was regarding the fraction of the cycle that the freewheeling diode conducts. The conversation explored two different explanations, one based on the assumption that the diodes in the rectifier share conduction equally and the other based on the classic concept of a freewheeling diode. The final answer was determined to be alpha/pie.
  • #1
jaus tail
615
48

Homework Statement


A half controlled single bridge rectifier is supplying an R-L load. It is operated at firing angle 'alpha'. Load current is continous. What is fraction of cycle that the freewheeling diode conducts?

Homework Equations


upload_2016-12-1_14-52-25.png

The Attempt at a Solution


Well I guess each diode will conduct for half the cycle like from 0 to pie and then from pie to 2 pie, the other diode will conduct.
So the answer must be 1/2. But book answer is alpha / pie.[/B]
 

Attachments

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  • #2
None of the 4 devices shown in your OP is a free-wheeling diode. Why is there no such diode shown in a question that apparently refers to it? :oldconfused:
 
  • #3
I thought FWD are the diodes D1 and D2. As per first diagram in the link:
http://www.technik-emden.de/~elmalab/projekte/ws9899/pe_html/ch06s1/ch06s1p1.htm

and book diagram:
upload_2016-12-1_17-7-20.png
 
  • #4
FWD in your attachment is a freewheeling diode.
 
  • #5
So it's a diode parallel to RL load with anode of diode towards up and cathode facing down.
Thanks.
 
  • #6
If load current is continuous, then the diodes in the rectifier must share conduction equally and your original answer would have to be right.

There is "freewheeling" operation due to the load inductance, otherwise load current could not be continuous. But I am not sure whether the 2 diodes that form half of the bridge are usually referred to as freewheeling diodes, though. I'll have to look at this more closely.

It's the diode directly across the load that I think of as the classic freewheeling diode.
 
  • #7
I tried with ur concept of FWD and got this answer as:
upload_2016-12-1_18-58-36.png

upload_2016-12-1_18-59-33.png


Thus i get the book answer.
Book has also given another explanation. They have taken fwd as diode D1 and D2.
They said that from
1) from alpha to pie, current flows through T1, load, D2
2) from pie to pie + alpha, current flows from T1 load, D1
So D1 is in freewheeling mode only in second case. Duration is pie + alpha - pie which is alpha. This happens in each half cycle of sine wave, so twice in full cycle.
Fraction is 2 * alpha divide by 2 * pie which gives alpha/pie.

But i like first explanation of mine better where ur concept of FWD is used. Thanks..
 

Attachments

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Related to Half controlled single bridge rectifier

What is a half controlled single bridge rectifier?

A half controlled single bridge rectifier is an electronic circuit used to convert alternating current (AC) to direct current (DC). It is composed of four diodes arranged in a bridge configuration, with two of the diodes being controlled by a switching device such as a thyristor or a transistor.

How does a half controlled single bridge rectifier work?

The rectifier works by alternating the direction of current flow through the load, resulting in a unidirectional flow of current. The controlled diodes are switched on and off to control the output voltage and current. During the positive half cycle of the AC input, the diode connected to the positive terminal of the AC supply conducts and charges the load capacitor. During the negative half cycle, the diode connected to the negative terminal conducts and discharges the capacitor, resulting in a smooth DC output.

What are the advantages of a half controlled single bridge rectifier?

The main advantage of this type of rectifier is that it allows for voltage and current control of the output, making it suitable for use in applications where variable DC power is required. It also has a simple and cost-effective design compared to other rectifier circuits.

What are the disadvantages of a half controlled single bridge rectifier?

One of the main disadvantages is that the controlled diodes have a limited switching speed, which can result in high switching losses and reduced efficiency. Additionally, the presence of the uncontrolled diodes can cause high ripple voltage in the output, which may not be suitable for sensitive electronic devices.

What are the common applications of a half controlled single bridge rectifier?

This type of rectifier is commonly used in industrial applications such as motor speed control, welding machines, and battery charging. It is also used in power supplies for electronic devices, where variable DC voltage is required.

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